In the US, hypertension is diagnosed by measuring blood pressure (BP) in the clinic by a healthcare provider or technician (attended clinic BP). However, this approach provides a poor estimate of a person's BP. Ambulatory BP monitoring (ABPM) measures BP automatically every 15 to 30 minutes outside of the clinic setting typically for 24 hours including while a person is awake and asleep. Although ABPM is considered to be the reference standard for diagnosing hypertension, it is not available in most clinics in the US and, when available, it is not tolerated by many patients. These issues highlight the need for new approaches for diagnosing hypertension. Canadian studies suggest that BP measured in the clinic using an automatic oscillometric device without an observer being present (unattended clinic BP) may be closer to awake BP on ABPM than attended clinic BP. However, these studies were uncontrolled with unattended clinic BP being measured after attended clinic BP; attended clinic BP was performed using a mercury sphygmomanometer, which is no longer the recommended for measuring BP; and often participants with very high attended clinic BP were enrolled. A recent analysis of data from the Systolic Blood Pressure Intervention Trial (SPRINT) did not find a difference between clinic BP when measured attended or unattended. However, participants did not have both attended and unattended BP measured at the same visit; all participants were taking antihypertensive medication; and data from ABPM were not available as a reference standard. In addition to elevated awake BP, elevated BP during sleep is associated with an increased risk of CVD. ABPM has been the only method that could measure sleep BP. A home BP monitoring (HBPM) device has recently been developed that can measure BP during sleep. In contrast to ABPM, these HBPM devices are worn for a shorter period of time (only during sleep) with fewer BP measurements, and thus may be better tolerated than ABPM. The goal of this study is to compare novel non-ABPM approaches to ABPM for measuring BP during the awake and sleep periods and diagnosing hypertension. For Aim 1, we will test whether unattended clinic BP provides a more accurate estimate of awake BP on ABPM than attended clinic BP. For Aim 2, we will determine the accuracy of a new HBPM device for measuring sleep BP. We will also evaluate whether the HBPM device is better tolerated than ABPM. For Aim 3, we will compare the associations of unattended clinic BP and attended clinic BP versus awake BP on ABPM and sleep BP on HBPM versus ABPM with left ventricular mass index and albuminuria. We will enroll 630 adults, not taking antihypertensive medication, with systolic BP of 110 to 159 mm Hg and diastolic BP of 70 to 99 mm Hg in New York, NY and Birmingham, AL. Participants will undergo both unattended and attended clinic BP, in random order, and ABPM and HBPM, also in random order. This rigorously designed study will provide important data on whether these new approaches can replace the need for conducting ABPM to assess awake and sleep BP and diagnose hypertension.